1. Field of the Invention
The present invention relates to a device which controls a copy operation for preparing a copy of data at a designated time in a storage device in accordance with an instruction from a host device, and a method thereof.
2. Description of the Related Art
As conventional methods for preparing a copy of data stored in a storage device (disk array device) which has one or more magnetic disk devices (disk drives), the following two methods exist:
(1) Method of Copying Through the Host Device
In this method, as shown in FIG. 1A, a host device 11 reads the data to be copied from a copy source logical unit 21 and writes this data to a destination logical unit 22. The logical unit is equivalent to a volume in a main frame system and is equivalent to a slice or a partition in an open system.(2) Method of Copying From the Storage DeviceIn this method, as shown in FIG. 1B, the host device 11 issues a copy instruction to the storage device 12. Upon receiving the instruction, the storage device 12 reads the data to be copied from the logical unit 21 and writes the data onto the logical unit 22.Thus, functions for performing a copy operation in a storage device are generally known, a function called OPC (One Point Copy) wherein this function is extended is also proposed (for example, see Japanese Laid Open Patent No. 2001-166974). The OPC operates according to the following steps, as shown in FIG. 1C.1. The storage device receives a copy instruction from the host device.2. The storage device assumes that the data copy was logically completed when the copy instruction was issued and immediately executes a copy completion response to the host device.3. The storage device physically copies the actual data from the copy source logical device to the copy destination logical device after executing the copy completion response.4. The storage device executes the following actions in regards to read/write access from the host device to an area wherein the copying of the actual data is not completed.A. Read access to an un-copied area of copy source: The storage executes normal operation, that is, the actual data is read normally.B. Write access to an un-copied area of copy source: After the existing data is copied to the copy destination, the designated actual data is written.C. Read access to an un-copied area of copy source: After the actual data is copied from the copy source, the copied data is read.D. Write access to an un-copied area of copy source: The designated actual data is written as is. Thereafter, this area is designated as already copied
By executing such operations, the time required for a copy operation, namely which is just until the response in item 2, described above, is returned to the host device, seems to become very short on the host device side. For example, even a copy of giga-bytes of data seems to take only several seconds to complete.
Japanese Laid Open Patent No. 11-345158 relates to a method of obtaining a dump in an information processing system comprising a disk device.
The following problem exists in copy control operation of the afore-mentioned conventional storage device.
OPC is a function which copies a snap shot of the entire or a part of the designated logical device (copy source, hereinafter referred to as Src) to the designated logical unit (copy destination, hereinafter referred to as Dest). In OPC, the physical copying of the entire designated range is executed at every booting up time is executed from Src to Dest. Since the load to the controller and the magnetic disk device is so heavy during physical copying that the performance of the entire storage device deteriorates, in comparison with when physical copying is not in process